One common type of compressor used for vehicular air conditioning utilizes a swash plate in a crank chamber. Some compressors of this type are responsive to both suction pressure and discharge pressure. These compressors effectively regulate the pressure in the crank chamber with respect to the suction pressure to alter the inclined angle of the swash plate in order to change the compressor's discharge volume.
The above type of compressor is disclosed in, for example, U.S. Pat. No. 4,428,718. This compressor is designed in such a way that a bellows expands to actuate a valve mechanism to decrease the area of a second passage between a suction chamber and the crank chamber. This occurs in response to variations in the balance between the suction pressure and atmospheric pressure. This could occur as the result of a decrease in the cooling load caused by lowering room temperature of the vehicle or as a result of a decrease in suction pressure caused by the compressor's fast rotation. A first passage between a discharge chamber and the crank chamber is opened by another valve mechanism to raise the crank-chamber pressure, thus increasing the difference between the crank-chamber pressure and the suction pressure. Accordingly, the pressure acting on the back of a piston increases and thereby reduces the stroke of that piston. The inclined angle of the swash plate consequently decreases which prevents reductions from being made in the suction pressure. This effectively reduces the overall displacement of the compressor.
In the above compressor, the discharge chamber communicates with the crank chamber through the first passage. The second passage guides the refrigerant gas and extends from the crank chamber to the suction chamber. The refrigerant gas, supplied from the discharge chamber to the crank chamber via the first passage, circulates in the crank chamber and then travels to the suction chamber from the crank chamber via the second passage. As the refrigerant gas passes through the crank chamber, a lubricating oil mist flows into the suction chamber. This moving refrigerant gas reduces the amount of the lubricating oil inside the crank chamber. This reduction of lubricating oil contributes to the wearing out of driving component portions of the crank chamber as for example the swash plate. Moreover, the lubricating oil that flows out of the compressor reduces the heat exchange effectiveness of the condenser and evaporator and thereby decreases the compressor's cooling efficiency.
It is therefore an object of the present invention to provide a swash plate type variable displacement compressor which can secure a lubricating oil in the crank chamber to maintain the high durability of the compressor's internal mechanism.
It is another object of the present invention to provide a swash plate type variable displacement compressor which has an excellent cooling efficiency.